docs(codes): Add (key) codes documentation

Create codes documentation for standardized keys.

Closes #218.  Fixes #308.  Ref #21.

docs/src/data/operating-systems.js

@@ -0,0 +1,38 @@
+/*
+ * Copyright (c) 2020 The ZMK Contributors
+ *
+ * SPDX-License-Identifier: CC-BY-NC-SA-4.0
+ */
+
+export default [
+  {
+    key: "windows",
+    className: "windows",
+    heading: "W",
+    title: "Windows",
+  },
+  {
+    key: "linux",
+    className: "linux",
+    heading: "L",
+    title: "Linux",
+  },
+  {
+    key: "android",
+    className: "android",
+    heading: "A",
+    title: "Android",
+  },
+  {
+    key: "macos",
+    className: "macos",
+    heading: "m",
+    title: "macOS",
+  },
+  {
+    key: "ios",
+    className: "ios",
+    heading: "i",
+    title: "iOS",
+  },
+];